Hey guys, i need the help of the folks who have tested their own N75 solenoid valves. What resistance should i get across the terminals? How is this valve supposed to function? I found an excerpt on a Laguna forum where it states: - At rest = full pass thru to wastegate - Energized = divert to intake duct This is where i am unsure if i have a dud valve or not. Are these valves meant to be an A or B ONLY switchover valve? Ie. Full pass thru (mode A/rest) or divert (mode B/energized). The reason i ask is i tested my valve using a vacuum pump and when i energized it, it didn't switch over to divert. If i were to explain it using a compressed air source instead of the vac pump, the air would be coming out of BOTH the 'to-wastegate' port and the 'to-intake duct' port of the N75... which might explain my inconsistent boost/throttle response. I hope some here has tested theirs before Or if you're curious, it only takes a few mins to pull the valve out for testing
I'm pretty sure the standard N75 doesn't use a closed loop boost control. I think it just bleeds off what it needs to to control boost.
The valve works using a PWM signal to control the 'duty cycle' of the valve. More open = more pressure to the wastegate actuator = less boost pressure. It is a closed system. It only uses the pipe in the intake hose to reference atmospheric pressure to my knowledge. If it doesnt get a signal it will be closed, and it will not divert to the intake duct. Rather, the spring in your wastegate actuator keeps the wastegate closed. The N75 valve only lets pressurised air through to overcome the actuator's spring force to open up the wastegate. Now I don't know if you have a 225 or 250/265/275, but on the 225 the boost will be solely controlled with the N75 valve. On the Mk3 RS, it will additionally be controlled using the throttle flap at the intake manifold, providing much better boost regulation.
it is exactly the opposite Tymen, the N75 bleed boost away, giving the actuator less reference pressure resulting in higher boost.
Tymen does the mk3 use the throttle to control boost all the time with the n75 or is it just a fail safe and shuts off to stop excess pressure entering the engine?
That is right: At rest full past thru wastegate. But because the wastegate start to open around 0.5 bar the n75 bleed boost to intake duct and your wastegate opens later. So when you floor it the n75 duty cycle is around 95%. And gradually decrase the duty cycle around the desired boost pressure. Would be the wastegate enough to controll the boost but in normal and in sport mode you need different amount boost. Thats why n75 and ecu can control...
Haha whoops, you're right :rolleyes:. Yes it does so at all time. I once put a manual boost controller instead of the N75 valve. While it did increase the boost pressure at the intake piping (before the throttle body), and I tried this up to 1.8bar, it did not increase the pressure at the intake manifold; the throttle flap just closes to not let the excessive boost go in there. All in all it results in a very nice boost regulation system which is much better than the 225s one.
Thanks for the replies, i've got a 265. Why would it need an atmospheric reference though? Isn't it purely a drain/place to dump the metered air? Hang on.. do our cars even have an airflow meter? I read somewhere that it doesn't... Would it be speed density then? This is all new to me - when i first encountered this valve poked into the intake duct, i thought to myself "that's a clever mount for the valve!". Then i read more into 3 port boost control solenoids. But with PWM control, there is no such thing as partial movement of the valve right? I think it should be a case of either straight to the wastegate or dumped into the intake. Either way, even when i applied power to the valve for longer than just a few quick taps it did not fully switch over
The valve switches from one output to the wastegate to two outputs wastegate and bleed off. The pwm controls how much is bled off. Your right it's open and close solenoid no partial like a stepper.
Exactly, it is constantly opening an closing at a verry high rate, just like injectors. all the tap to the inlet does is route the air back. Could aswell pul the hose off and let it vent to atmosphere
Forgive my curiosity but why would it switch to two outputs if the PWM control is supposedly precise enough to handle it? James, is this based on your own observations when you tested yours? Thing is, every time i pull the N75 out and then refit it, the car goes like a jack rabbit for the first drive then it feels sporadic again
It opens the second port to bleed off excess boost presure going to the actuator. That's how this system works. I've fitted an hks closed loop boost controller to mine.
The way i see it is the wastegate actuator is like a tyre. As in it's airtight so how hard it is depends on how much pressure is inside it. Since it's a 7psi actuator and the compressor side of the turbo would probably be in excess of 7psi, would it not 'inflate' the actuator even more if any pressurised reference air was permitted to reach it? Unless... testing or demonstrating its function using vacuum instead of pressure is not going to create the same conclusion. If pressure was applied via the reference port and the solenoid valve energized with a vacuum gauge attached to the wastegate port, a venturi would be created and thus draw out air from the wastegate circuit eh?
